The present application claims priority to Japanese Application No. P11-259098 filed Sep. 13, 1999, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a semiconductor device and its manufacturing method, especially suitable for application to a semiconductor integrated circuit device having multi-layered wiring.
2. Description of the Related Art
Along with progressively high integration of elements for semiconductor integrated circuit devices, wiring techniques are moving, toward further microminiaturization and multi-layered structures. It is said, for example, that logical LSI having the design rule of 0.18 micron class requires multi-layered wiring of six or more layers. Therefore, multi-layered wiring processes are getting more and more important in manufacturing processes of semiconductor integrated circuit devices.
However, developments of microminiaturization and multi-layered structures of wiring invited a new problem. That is, since developments of microminiaturization and multi-layered structures of wiring make level differences of inter-layer insulating films large and sharp, it is difficult to make a metal wiring pattern thereon freely from breakage at different levels or other faults.
To solve this problem, chemical mechanical polishing (CMP) has been introduced and used in a wiring process. This method is configured to smooth the surface of an inter-layer insulating film completely by CMP and thereafter make metal wiring thereon. Alternatively, the method is configured to make a via hole in the inter-layer insulating film for electrically connecting upper and lower wiring layers. The method then buries a metal film in the via hole, and subsequently polishes and smooths the metal film by CMP to make a plug in the via hole.
Here is explained a conventional chemical mechanical polishing unit. An example thereof is shown in FIG. 1. As shown in FIG. 1, the chemical mechanical polishing unit includes, as its major components, an abrasive plate 103 which has an abrasive cloth 101 fixed to it and rotates in the arrow-marked direction 102 in FIG. 1 with an external driving force; a carrier 106 which holds a substrate 104, such as a wafer, to be polished and urges it onto the abrasive cloth 101 with a polishing pressure, and rotates in the arrow-marked direction 105 in FIG. 1 with an external driving force. The chemical mechanical polishing unit also includes a slurry supply system 107 which supplies an abrasive agent, i.e. slurry, prepared by suspending abrasive particles of silica or alumina, for example, in water containing a pH adjusting agent. From one end of a slurry supply opening 108 attached to the slurry supply system 107, slurry 109 is poured down to near the rotation center of the abrasive plate 103, and the poured slurry 109 is spread over the abrasive cloth 101 due to a centrifugal force produced by rotation of the abrasive plate 103. Then, while supplying the slurry 109 in this manner, both the abrasive plate 103 and the carrier 106 are rotated to rub the substrate 104 with the abrasive cloth 101 and thereby grind the surface of the substrate 104. At that time, depending upon the material to be polished, namely, insulating film or metal film, chemical mechanical polishing is effected in a basic or acidic atmosphere.
Chemical mechanical polishing is currently the most effective smoothing method, but it still involves various problems. One problem is the difficulty of burying a metal in via holes by sputtering that has been used for making a metal film, because of progressive reduction of the diameter of the via holes due to microminiaturization. Recently, therefore, electrolytic plating or CVD is often used for making metal films instead of sputtering. On the other hand, there is an active trial to use copper (Cu) having a low specific resistance, high resistance to electro migration and high reliability as wiring metal instead of aluminum (Al) alloys heretofore used. However, when Cu is used to make a film by electrolytic plating, post-plating configuration is not yet satisfactory. More specifically, as shown in FIG. 2A, in the case where a Cu film 204 is made by electrolytic plating after via holes 203 are made in an inter-layer insulating film 202 stacked to cover a base-layer wiring 201 of a substrate, not shown, an unevenness is produced on its surface, reflecting the density of the via holes 203 made in the inter-layer insulating film 202. Therefore, if the Cu film 204 is polished by using slurry of a suspension type normally used for chemical mechanical polishing, the liquid of the slurry forms a thin liquid film between the substrate to be polished and the abrasive cloth, and cause a so-called hydro plane phenomenon. This is similar to the phenomenon that, when a car runs on a highway in rain, rain makes a thin liquid film between the road surface and tires and makes tires liable to slip. Here is remarked the problem that, due to this hydro plain phenomenon, a kind of gap is produced between the abrasive cloth and the substrate and disturbs smoothing by polishing, and the surface configuration of plugs 205 of the Cu film left in the via holes 203 after polishing remain uneven without being smoothed sufficiently. As a result, if an overlying inter-layer insulating film is formed after the plugs 205 are made, undesirable configuration of the plugs 205 and failure to bury the upper plug material in the via holes, for example, might decrease the production yield of semiconductor integrated circuit devices.
Under the circumstances, active studies are being made toward CMP not using slurry. Since this method does not use slurry, the above-mentioned problem does not occur. However, in simple words, this method is similar to grind a surface with a file, and it has the drawback that the evenness of the surface after polishing is inferior to that by CMP using slurry.
Under the above-explained background, for the next-generation semiconductor integrated circuit devices, there has been a demand for chemical mechanical polishing capable of accomplishing global surface evenness while accomplishing local surface evenness as well.
It is therefore an object of the invention to provide a semiconductor device and its manufacturing method capable of accomplishing global surface evenness while also accomplishing local evenness by removing defects of local surface configuration.
A more general object of the invention is to provide a semiconductor device and its manufacturing method capable of optimizing polishing and obtaining well-smoothed configuration.
To solve the above-indicated problems involved in the conventional techniques, the Inventor made a hard study. Its outline is explained below.
Today""s chemical mechanical polishing uses suspension-type slurry for polishing from its starting process. Therefore, if the workpiece to be polished has an unevenness on its surface when polishing is started, the suspension-type slurry causes the above-indicated hydro plain phenomenon between the surface to be polished and the abrasive cloth, and polishing progresses while uneven portions particularly requiring polishing on the workpiece to be polished does not contact the abrasive cloth sufficiently. As a result, the surface configuration after polishing remains insufficient in evenness. Thus, the Inventor made various researches, and found that the surface after polishing was made more compact and smooth by conducting rough smoothing by using non-suspension-type slurry in the first step of polishing so as to remove projecting portions only by physical motions of abrasive particles and thereafter executing polishing by using suspension-type slurry.
The inventor made further studies, and realized, as a result of again reviewing the above-mentioned suspension-type slurry and non-suspension-type slurry from the standpoint of the degree of distribution of abrasive particles in the slurry, that it was effective for better smoothing, in a more general sense, to conduct some occurrences of chemical mechanical polishing by using different kinds of slurry that are different in the degree of distribution of abrasive particles, depending upon the surface configuration of the workpiece to be smoothed or the material of the work piece. More specifically, in the case where a large unevenness exists on the surface of a workpiece to be polished, for example, it is effective to first use slurry with a small amount of abrasive particles (its utmost example is non-suspension-type slurry) for chemical mechanical polishing to remove projections and roughly smooth the surface, and thereafter using slurry with a larger amount of abrasive particles (for example, suspension-type slurry similar to the conventional one, for example) to progress the polishing.
This invention has been made through those researches and studies of the Inventor.
According to the first aspect of the invention, there is provided a method for manufacturing a semiconductor device comprising the step of:
conducting chemical mechanical polishing in a plurality of separate steps by using different type of slurry which are different in degree of dispersion of abrasive particles.
According to the second aspect of the invention, there is provided a semiconductor device comprising a substrate whose surface is smoothed by chemical mechanical polishing using different types of slurry which are different in degree of dispersion of abrasive particles.
The xe2x80x9cdegree of dispersion of abrasive particlesxe2x80x9d indicates uniformity of distribution of abrasive particles in slurry. When abrasive particles distribute in slurry completely uniformly, the degree of dispersion of abrasive particles is the largest, and as the distribution becomes nonuniform, degree of dispersion of abrasive particles becomes smaller. It is a general tendency that abrasion by physical actions of abrasive particles becomes dominant as the degree of dispersion of abrasive particles in slurry becomes smaller.
In a typical mode of the present invention, chemical mechanical polishing is conducted over a plurality of times while increasing the degree of dispersion of abrasive particles in slurry from one step to another. More specifically, in the first chemical mechanical polishing, for example, non-suspension-type slurry is used. Most typically, chemical mechanical polishing is first conducted by using non-suspension-type slurry, and chemical mechanical polishing is next conducted by using suspension-type slurry.
According to the intention having the above-summarized configuration, by performing chemical mechanical polishing over a plurality of times by using different kinds of slurry which are different in degree of dispersion of abrasive particles, slurry with optimum degree of dispersion of abrasive particles can be selected for polishing from time to time upon the start of polishing and during progress of polishing, depending upon the surface unevenness and the material of the workpiece to be polished, and optimum polishing is ensured. Especially, by first conducting chemical mechanical polishing by using non-suspension-type slurry, the hydro plain phenomenon can be prevented, and projections on the surface of the workpiece can be removed exclusively by physical motions of abrasive particles to roughly smooth the surface. Then, by next conducting chemical mechanical polishing, using suspension-type slurry, the surface of the workpiece can be smoothed to a compact, excellent configuration.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.